Belles, Frank E.

Brabbs, Theodore A.

Zlatarich, Steven A.

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CASE FILEso925 
44 1 COPY 
Reprinted from the JOURNAL OF CHEMICAL PHYSICS, Vol. 33, No. 1, 307-308, July, 1960

Printed in U. S. A.
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date stamped on b2ck cover. 
Limitations of the Reflected-Shock FLEASE RETURN TO 
Technique for Studying Fast ChenlJ"j DISTRWUT!ON SECI ON Reactions
LAiGLEY RESE1tCH CENTER THEODORE A. BRABBS, STEVEN A. ZLATARICH, 
AND FRANK E. BELLES	 NATIONAL AEWiAUTIcS AND 
Lewis Research Center, National Aeronautics and Space 
CDACE ADMINISTRATION Administation, Cleveland, Ohio 
(Received February 26, 1960)	 Vigi 
U
SE of the region behind a reflected shock wave for 
chemical kinetic studies presupposes that the 
temperature is known. Three easily measured proper-
ties are available from which the temperature can be 
calculated with one-dimensional theory: incident Mach 
number M3, reflected Mach number M, (defined in 
each case as wave velocity divided by sound speed at 
initial conditions), or reflected shock pressure p5. 
Two previous articles have dealt with the validity of 
such calculations for the case of argon. Strehlow and 
Cohen' used measured Mrs to compute temperatures 
300-500°K lower than those computed from measured 
M5 . Skinner' measured p5 and found it to give tempera-
tures only 30-50°K lower than those calculated from 
M8 . It was believed that further information bearing on 
this point might be derived from simultaneous measure-
ments of all three properties, also in argon. 
The shock tube used is made of 2 12 -in. i.d. stainless-
steel tubing, with a 15-ft expansion section and a 521-ft 
driver. Incident and reflected shock velocities were 
measured with two Berkley time-interval meters 
adjusted to different trigger sensitivities and operated 
by miniature piezoelectric pressure transducers.' Pres-
sures were measured with a SLM 4 transducer placed 6 
in. from the end plate. This pickup, which has the prop-
erty of static response, was calibrated by means of a 
dead-weight gauge. The p5 measurements were taken 
from photographs of oscilloscope traces and, owing to 
finite line widths and a slight ringing of the pickup, 
they contain an uncertainty of about 2%. 
Both incident and reflected shock velocities were 
measured over two regions in the shock tube, in separate 
experiments. The near region had two probes located 
6 and 10 in. from the end plate, while the far region had 
the probes 6 and 25 in. from the end plate. The greatest 
uncertainty existed in measurements taken of the 
velocity of the fast-moving incident shock as it tra-
versed the 4 in. of the near position; it was about 10/0.
THEORETICAL
oM,(FAR REGION)
O	 M,,NEAR REGION) 
PRESSURE MEASUREMENTS 
FIG. 1. P51 values for argon calculated from M8, Mrs (near 
region), M,8 (far region) and pressure measurements. 
Figure 1 shows all the data plotted in terms of M. 
against the ratio P51 (p5/p1 , where the initial pressure 
' was 150 mm Hg in all cases). The dashed curve is 
simply the ideal one-dimensional relation between 
P51 and M8 . The other two curves show P51 computed 
from measured Mr. against simultaneously measured 
M. for the near and far regions. If the reflection were 
ideal, all three curves would coincide. However, that 
the curve for the far region lies closer to theory than 
that for the near region, and that both lie below the 
ideal, could be explained by a deceleration near the back 
wall, followed by the measured acceleration. Such a 
phenomenon is predicted by Mark' for argon between 
M8 = 1.4 and 2.8. Since most of the data are not in this 
Mach number region, the shock speed variations herein 
encountered must be a result of another phenomenon.
t.ç 
2	 . 4,E T1' E RS TO 
The measured values of P51 are deotd by crosses 
in Fig. 1; these are pressures corresponding to the verti-
cal rise of the oscilloscope trace when the reflected 
shock passes the pickup. It can be seen that these 
measured P51's fall essentially on the curve for re-
flected shock pressures calculated from the far position 
velocities, even though the pressure pickup was at the 
near position. This concord between the pressure 
measured at the 6-in, position and the far-position 
reflected-shock speed indicates that the wave, as it 
passed the SLM pickup, was traveling at a speed near 
this average value. This would mean that the pressure, 
as well as the shock speed, depends upon the location 
selected to make the measurement. The departures 
of measured P51 's from the ideal, when translated to 
temperature, were averaged for M8 ranges 2.5-3.0 
and 3.0-3.5 and amounted to about 40° and 60°K 
respectively, just as Skinner concluded.
THE EDITOR 
Following the initial pressure jump, the traces show a 
continued slow rise, such as Skinner described. At 500 
jzsec after the jump, many of the traces indicated a 
pressure slightly larger than that expected for an ideal 
reflection. 
In conclusion, it appears that the values of both Mrs 
and p5 depend upon the position selected to record the 
measurement. It is believed that reaction temperatures 
derived from pressure measurements are better than 
those from Mrs measurements, because the pressure 
reflects the time-temperature history over the region 
in question. 
'R. A. Strehiow and A. Cohen, J. Chem. Phys. 30, 257 (1959). 
2 G. B. Skinner, J
.
 Chem. Phys. 31, 268 (1959). 
Made by us, using Clevite Corporation's PZT-5 crystal 
elements. 
Purchased from Kistler Instrument Company, Model No. 680. 
Herman Mark, "The interaction of a reflected shock wave 
with the boundary layer in a shock tube," NACA TM 1418 
(1958).


Limitations of the Reflected-Shock Technique for Studying Fast Chemical Reactions

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